The present invention relates to a vacuum fluorescent display in which cathodes, grids, and anodes coated with phosphors are accommodated in a vacuum-evacuated envelope.
FIG. 6 shows a conventional flat type vacuum fluorescent display. Referring to FIG. 6, a vacuum fluorescent display 100 includes a substrate 111, an at least partly transparent front glass plate 112, and a glass spacer 113 arranged between the substrate 111 and front glass plate 112. The substrate 111, front glass plate 112, and glass spacer 113 are adhered to each other through frit glass portions 114 and 115 to form an envelope 101. In the envelope 101, wiring lines (not shown) are printed on the substrate 111, a plurality of anodes are arranged on the wiring lines through an insulating layer (not shown), and phosphors are attached to the anodes. The plurality of anodes form display portions 121 that can display a predetermined pattern. The plurality of anodes are disposed in, e.g., a matrix, and are indicated as display portions 121 formed of a large number of dots in FIG. 6. Strip-like or rectangular grids 122 are arranged above the display portions 121. For example, the grids 122 are formed of a plurality of segment grids 122a vertically provided substantially parallel to each other to cover the display portions 121, and support members 122b for the segment grids 122a. A plurality of cathodes 123 are arranged above the grids 122. For example, at least a plurality of filament cathodes 123 disposed in a direction perpendicular to the longitudinal direction of the grids 122 are accommodated.
The filament cathodes 123 are extended by a pair of filament supports 124 and 125, and led outside the envelope 101 through lead pins 126 and 127 as part of the filament supports 124 and 125, to supply power from the outside.
In this example, bases 124a and 125a of the filament supports 124 and 125 are disposed near the two ends in the longitudinal direction on the substrate 111 toward the substrate 111. The filament cathodes 123 are built by extending portions 124b and 125b vertically provided to the bases 124a and 125a. The lead pins 126 and 127 are led outside the envelope 101 through the gap between the substrate 111 and glass spacer 113.
The display portions 121 and grids 122 are connected to part of the wiring pattern printed in advance on the surface of the substrate 111. Pads 129 formed at one end in the short-side direction of the substrate 111 are connected to the other end of the wiring pattern. The pads 129 are connected to lead pins 128 led outside the envelope 101 through the gap between the substrate 111 and glass spacer 113. External power and signals necessary for operating the vacuum fluorescent display 100 are input to the display portions 121 and grids 122 through the lead pins 128 and pads 129.
In the vacuum fluorescent display 100, electrons extracted from the cathodes 123 pass through the grids 122, are accelerated by the anodes, and bombard on the phosphors applied to the anodes of the display portions 121. The bombardment on the phosphors causes light emission. This structure is described well in, e.g., Japanese Patent Laid-Open Nos. 05-275033 and 08-017367.
In the conventional vacuum fluorescent display 100 described above, as the bases 124a and 125a of the filament supports 124 and 125 are arranged on the substrate 111, regions to arrange the filament supports 124 and 125 must be reserved on the substrate 111, and be spared from that region on the substrate 111 where the display portions 121 are to be arranged. In other words, that region on the substrate 111 where the display portions 121 can be arranged is limited to a region obtained by excluding from the substrate 111 the regions to dispose the filament supports 124 and 125. It is difficult to further enlarge the display region of the vacuum fluorescent display 100.